Abstract: The technology of spacecraft’s space on-orbit service has received increasing attention. The basis of space on-orbit service is spacecraft rendezvous technology, and the essence of spacecraft rendezvous is the approach of the chaser to the target in close range. During the process of approaching the target, the chaser should avoid collisions with accessories such as the solar panel and antenna of the target. In order to ensure the safety of the approximation process, an optimal control strategy for spacecraft approaching along a designated straight direction is proposed. The relative motion model between the two spacecraft with arbitrary eccentricity orbit described by nonlinear TH (Tschauner-Hempel) equation is established. The coordinate system of linear approximation motion is introduced, and the optimal control acceleration of the chaser is derived according to the Hamiltonian equation and the characteristics of linear direction approximation motion. The chaser spacecraft can not only approach the target along a designated straight direction according to the mission requirements, but also ensure the optimal energy. In order to eliminate the interference factors that affect the linear approximation, the proportional differential control law is used to correct the derived control acceleration in the non-linear direction. In order to verify the effectiveness of the proposed control strategy, two sets of scenarios are set up for numerical simulation, which are the linear approximation of the chaser along the velocity direction of the target and the linear approximation along the radial direction of the target. The simulation results show that the proposed control strategy can realize the chaser approaching the target along the designated straight direction, which has good engineering applicability and provides a new idea for improving the success rate and safety of spacecraft space on-orbit service.

Key words: spacecraft rendezvous, approach along straight direction, optimal control, space on-orbit service, proportional differential